Waterspouts came ashore in Plymouth last week and became a small tornado that caused minor damage, the National Weather Service said Monday. The service said three waterspouts formed off Manomet at 4:06 p.m. Tuesday and rapidly moved ashore, causing minor damage at White Horse Beach two minutes later. “By the rules, any time a waterspout moves onshore and causes damage, we have to go ahead and classify it as a tornado,” Weather Service meteorologist Alan Dunham said. The tornado’s path was 45 yards long and 15 yards wide. Winds whipping as fast as 65 miles per hour ripped a window off its hinges, damaged a beach umbrella and some awnings, and hurled sand and other debris into the air higher than nearby beachside condos, the Weather Service reported.